My 93 C1500 has 216k miles on it now. The first 40k of its life, it was a work truck, owned by a construction company. Then my dad bought it and ran it up to about 95k miles. This was near pittsburgh PA. I think my dad changed the transmission fluid once when he had it. This truck was used pretty heavy, it was a winter truck for my dad and he used it to haul the coal trailer during the winter and misc things during summer. It was cared for well, but used. I bought it from him and it had around 95k miles on the clock. I have been pretty good about keeping up with transmission changes as the fluid always had a burnt type smell and was brownish. Over the years it has seen some pretty easy living. I drove it back and forth to school and to work. I live in Mid NC so it is pretty flat and alot if interstate driving. I have used it a few times to haul atvs, mulch, rock, dirt and helping people move. I changed it at these intervals. 128k,135k, 140k, 162k, 210k. I try to do it every 30k but it dont seem to be working out that way. You can see early on i changed it a lot trying to get that nasty fluid out. Truck still runs good, but i notice when im pulling a boat and accelerating hard, it slips a little going into second. Hopefully i can baby it along for a while yet.